Polyolefins are considered among the most difficult polymeric materials to treat because they have poor adhesive properties and high chemical barrier responses. In this paper, an in-depth study is reported for the low pressure plasma (LPP) treatment of neutral polypropylene to improve adhesion properties. Changes in wettability, chemical species, surface morphology and roughness of the polypropylene surfaces were evaluated by water contact angle measurement, X-ray photoelectron spectroscopy and, furthermore, atomic force microscopy (AFM). Finally, the bonded joints were subjected to tensile tests, in order to evaluate the practical effect of changes in adhesion properties. The results indicate that plasma is an effective treatment for the surface preparation of polypropylene for the creation of bonded joints: contact angles decreased significantly depending on the plasma-parameter setup, surface morphology was also found to vary with plasma power, exposure time and working gas.

Friction stir welding (FSW) is a solid-state technique, which has assumed an increasingly important role in automotive, naval, and aeronautical industry over the years. Nowadays, thanks to its several benefits, FSW is used to weld any type of metallic, polymeric, or composite material. In recent decades, adhesive bonding has also enhanced relevance due to a request for much lighter structures to increase performance without increasing fuel consumption. From a mechanical perspective, welding has a high tensile strength despite a low fatigue resistance through the lack of joint elasticity. Therefore, the aim of this study is to investigate and compare static and dynamic behavior of welded, weld-bonded, and adhesive-bonded joints. After choosing the most suitable adhesive, surface preparation, consisting of sandblasting, was carried out. First of all, on the basis of previous experience in FSW, the process parameters of hybrid welding were determined. Both quasi-static and dynamic behavior of welded, adhesive-bonded, and weld-bonded joints, made in overlapped configuration, were then compared. Experimental tests showed that the adhesive limits the negative effect, due to the presence of the structural notch of FSW overlapped joints.

Fiber laser techniques are increasing their use in many applications, including modification of material surface properties. In particular they are often used for materials’ marking as a non-contact processing. In spite of this, the impact of the laser beam on the surface causes metallurgical and morphological changes. The developments during the laser-material interaction can also affect other surface properties, especially corrosion properties which are crucial in the case of Iron-Nickel alloys. Effect of laser marking on a Fe-Cr-Ni alloy using a Tm-fibre laser (IPG Photonics TRL1904; maximum power: 50W, wavelength: 1904 nm), is described in this paper. In order to evaluate the effect of the laser on corrosion properties a specific ageing test in salt spray has been performed. Moreover, superficial morphology analyses have been performed on samples before and after corrosion tests. Possibilities and limitations of laser marking on these alloys have been discussed, in particular from the point of view of the marked surface corrosion resistance preservation.